Plate-like magnetoplumbite ferrite particles for magnetic recording and process for producing the same

Abstract

Disclosed herein are Ba-containing plate-like magnetoplumbite type ferrite particles for magnetic recording containing ions of one metal (II) selected from Ni and Zn and ions of one metal (IV) selected from Ti, Sn and Zr, and having zinc incorporated as a solid solution close to the particle surface and the change of coercive force of said particles at a temperature of -20° to 120° C. in the range of -0.5 to +0.5 Oe/°C., and a process for producing the same.

What is claimed is: 
     
       1. A process for producing Ba- and/or Sr-containing plate-like magnetoplumbite ferrite particles for magnetic recording, which comprises the steps of: (a) subjecting an alkaline iron hydroxide (III) suspension containing ions of one metal (II) selected from Ni and Zn in an amount of 4.0 to 14.0 atom % based upon Fe (III) ions, ions of one metal (IV) selected from Ti, Sn and Zr in an amount of 2.0 to 14.0 atom % based upon Fe (III) ions and Ba and/or Sr ions to an autoclaving treatment at a temperature in the range of 150° to 330° C. to produce Da- and/or Sr-containing plate-like magnetoplumbite ferrite particles containing the metals (II) and (IV);   (b) suspending said particles in a zinc-containing aqueous solution of pH 4.0-12.0 to obtain the plate-like magnetoplumbite type ferrite particles containing the metals (II) and (IV) and having a hydroxide of zinc deposited on the particle surface;   (c) filtering said particles;   (d) heating and calcining said particles at a temperature in the range of 600° to 900° C. so that from 0.2 to 6.0% by weight zinc is incorporated as a solid solution close to the particle surface, said particles having an average diameter of 0.05 to 0.25 μm, a coercive force of 500 to 1,000 Oe, a magnetization of not less than 50 emu/g, an erasing characteristic value of not less than 25 dB, and a change of coercive force at a temperature of -20° to 120° C. in the range of -0.5 to +0.5 Oe/°C.     
     
     
       2. The process of claim 1 wherein the particles are heated in step (d) in the presence of at least one flux selected from halides and sulfates of alkali metals and alkali earth metals. 
     
     
       3. Ba- and/or Sr-containing plate-like magnetoplumbite ferrite particles for magnetic recording containing ions of one metal (II) selected from Ni and Zn and ions of one metal (IV) selected from Ti, Sn and Zr, the metal (II) being present in an amount of from 4.0 to 14.0 atom % based on Fe (III) ions contained in the ferrite and the metal (IV) being present in an amount of from 2.0 to 14.0 atom % based upon the Fe (III) ions contained in the ferrite, said metal (II) and said metal (IV) substituting for part of the Fe (III), and having zinc incorporated as a solid solution close to the particle surface, said particles having an average diameter of 0.05 to 0.25 μm, a coercive force of 500 to 1,000 Oe, a magnetization of not less than 50 emu/g, an erasing characteristic value of not less than 25 dB, and a change of coercive force at a temperature of -20° to 120° C. in the range of -0.5 to +0.5 Oe/°C., said particles prepared by a process which comprises the steps of: (a) subjecting an alkaline iron hydroxide (III) suspension containing ions of one metal (II) selected from Ni and Zn in an amount of 4.0 to 14.0 atom % based upon Fe (III) ions,   ions of one metal (IV) selected from Ti, Sn and Zr in an amount of 2.0 to 14.0 atom % based upon Fe (III) ions, and Ba and/or Sr ions to an autoclaving treatment at a temperature in the range of 150° to 333° C. to produce Ba- and/or Sr containing plate-like magnetoplumbite ferrite particles containing the metals (ii) and (IV);   (b) suspending said particles in a zinc-containing aqueous solution of pH 4.0-12.0 to obtain the plate-like magnetoplumbite-type ferrite particles containing the metals (II) and (IV) and having a hydroxide of zinc deposited on the particle surface;   (c) filtering said particles, and   (d) heating and calcining said particles at a temperature in the range of 600° to 900° C. so that from 0.2 to 6% by weight zinc is incorporated as a solid solution close to the particle surface.